CN112226645B

CN112226645B - Lead-free-cutting brass and preparation method thereof

Info

Publication number: CN112226645B
Application number: CN202010915292.7A
Authority: CN
Inventors: 叶东皇; 郑恩奇; 巢国辉; 傅杰
Original assignee: Ningbo Jintian Copper Group Co Ltd
Current assignee: Ningbo Jintian Copper Group Co Ltd
Priority date: 2020-09-03
Filing date: 2020-09-03
Publication date: 2021-11-30
Anticipated expiration: 2040-09-03
Also published as: CN112226645A

Abstract

The invention relates to lead-free-cutting brass which is characterized by comprising the following components in percentage by mass: 58.1 to 62.0%, Sn: 0.5 to 1.5 percent of Ni, less than or equal to 0.1 percent of Fe, less than or equal to 0.09 percent of Pb, and 0.003 to 0.20 percent of element X, the balance being Zn and inevitable trace elements, wherein the element A is at least one selected from 0.02 to 0.5 percent of Te, 0.02 to 0.4 percent of Mg, 0.02 to 0.15 percent of P and 0.1 to 1.5 percent of Si, and the element X is selected from Ti and/or Er. The invention reduces the cost of the lead-free-cutting brass by controlling the content of Cu, and changes the phase composition of the brass alloy by adding Sn and elements A and X, thereby realizing the combination of drilling performance and riveting performance.

Description

Lead-free-cutting brass and preparation method thereof

Technical Field

The invention belongs to the technical field of copper alloy, and particularly relates to lead-free-cutting brass and a preparation method thereof.

Background

For a long time, lead brass materials are used for processing various terminal parts in the industries of electric appliances, communication, instruments, medical appliances and the like. As is known, lead brass has good machinability, but Pb is harmful to many organs and physiological functions in the human body, and therefore, the eu rohs2.0 directive requires a Pb content in electronic and electrical products of less than 0.1%. Currently, the european union RoHS2.0 is exempted from Pb, the exemption period is due at 7/21/2021, all the electric and electronic products except the medical and monitoring equipment need to meet the regulation and control requirements of 10 harmful substances from 7/22/2021, and the medical and monitoring equipment needs to meet new requirements from 7/22/2021, which means that 6 harmful substances (Pb is one of them) in RoHS cannot pass through the european union customs.

The alloy grades already applied in the lead-free copper market mainly include: bismuth brass represented by HBi59-1, and silicon brass represented by C69300. The bismuth brass has large self-cracking tendency, the waste is difficult to recycle and the like; the problems of poor welding performance, high cost (the content of Cu is more than 70wt percent) and the like exist in silicon brass, so that the application of bismuth brass and silicon brass is always limited, and lead-free alternative materials are urgently needed to be found in lead brass products exported to regions of European Union and the like when the exemption period of RoHS2.0 containing Pb comes. Along with the enhancement of environmental awareness and the attention to health of people, the unleaded copper material is an inevitable development trend, the market demand for unleaded copper is getting bigger and bigger, especially the terminal market, the market capacity is large, and because the cutting processing needs to be carried out on a high-speed lathe, the requirement of customers on the cutting performance of the copper material, especially the drilling performance of drill holes with the diameter of less than 4mm, is a market segment with the greatest development potential of the unleaded copper material, and certain unleaded copper processing parts are easy to crack during riveting, so the riveting performance of the unleaded copper alloy needs to be further improved.

Disclosure of Invention

The invention aims to solve the first technical problem of providing the lead-free-cutting brass with good drilling performance and riveting performance.

The technical scheme adopted by the invention for solving the first technical problem is as follows: the lead-free-cutting brass is characterized by comprising the following components in percentage by mass: 58.1 to 62.0%, Sn: 0.5 to 1.5 percent of Ni, less than or equal to 0.1 percent of Fe, less than or equal to 0.09 percent of Pb, and 0.003 to 0.20 percent of element X, the balance being Zn and inevitable trace elements, wherein the element A is at least one selected from 0.02 to 0.5 percent of Te, 0.02 to 0.4 percent of Mg, 0.02 to 0.15 percent of P and 0.1 to 1.5 percent of Si, and the element X is selected from Ti and/or Er.

Cu is a matrix element of the alloy, the copper content is controlled within 58.1-62.0%, on one hand, the copper content is within the control range, the phase composition of the copper is alpha + beta dual-phase brass, the alpha phase is a face-centered cubic structure solid solution based on Cu, the alpha phase is soft, the plasticity of the alloy is mainly improved, the alloy has excellent processing performance in the subsequent processing process, particularly the subsequent riveting performance is influenced, the beta phase is a body-centered cubic structure solid solution based on a CuZn compound, the property is hard and brittle, the strength is higher, but the plasticity is poor, and the cutting performance, particularly the drilling performance of the alloy is improved to a certain extent.

Sn improves the mechanical property and the corrosion resistance of the alloy in the brass alloy, the zinc equivalent coefficient in the brass is +4, after the Sn element is added, the beta phase region of the brass alloy is enlarged, the cutting property of the alloy is improved, Sn can be diffused to the surface of the brass alloy to form a Sn-containing passive film, and the corrosion resistance of the alloy is improved, but the brittle beta phase is increased due to the over-high Sn content, a cutter is easy to damage and is easy to crack by riveting and pressing during cutting, and therefore, the Sn content is controlled to be 0.5-1.5%.

The solubility of Te in Cu is extremely low, and Te forms Cu with Cu₂The Te brittle compound precipitates from grain boundaries during solidification, and the cutting performance of the brass alloy can be improved. When the addition of Te is less than 0.02%, the effect of improving the cutting performance is not obvious.

The solid solubility of Mg in Cu is very low, and the hard and brittle Mg-containing compound is distributed in the brass matrix in a spherical shape, so that the cutting of brass is facilitated, and the cutting performance of the lead-free brass is improved. Mg is added into brass, so that the corrosion resistance of the brass is reduced while the cutting performance is improved, therefore, the addition amount of Mg is not high enough to exceed 0.4 percent generally, and when the content of Mg is less than 0.02 percent, the effect of improving the cutting performance is not obvious.

The solubility of P in Cu is very small, and supersaturated P can form Cu with Cu₃The brittle phase P forms dispersed particles distributed in an alloy matrix, so that the cutting performance of the alloy can be improved, but when the P is excessive, the brittleness of brass is increased, the cold processing performance and the riveting performance of the material are deteriorated, the addition amount of the P cannot exceed 0.15%, and when the addition amount of the P is less than 0.02%, the effect of improving the cutting performance is not obvious.

The zinc equivalent coefficient of Si in the brass is +10, and after the Si element is added, the beta phase region of the brass alloy is enlarged, so that the brass alloy is extruded at a lower extrusion temperature, and the free-cutting tissue morphology with the hard brittle beta phase as a matrix and the soft alpha phase embedded therein can be obtained. Further, Cu is formed when the Si content in brass exceeds 0.10%₉Brittle compounds of Si and ZnSi for improving brassWhen the content of Si in the two-phase brass exceeds 1.5%, the alloy forms more silicide, thereby deteriorating the cold processing performance and riveting performance of the brass and increasing the cutting resistance. In the brass, when Si and Fe or Mn coexist, an iron-silicon-manganese wear-resistant phase is formed, so that the cutting resistance is increased, the cutter wear is accelerated, and the cutting performance of the brass is deteriorated. The addition of Si can also improve the hot forging performance of the alloy. Therefore, in the present application, the content of Fe is controlled to 0.1% or less.

In the process of machining deformation, the finer the crystal grains are, the better the coordination of uneven deformation during cutting is, the better the cutting performance is, and the surface roughness of the workpiece after cutting is low. Formation of Cu from Ti and Cu₃The Ti high-melting point compound is distributed in the brass alloy matrix, and plays a role in nucleation when the alloy is solidified and recrystallized, thereby refining grains. The addition of a trace amount of rare earth element Er during the smelting of the brass is beneficial to the embedding of the alpha phase in the brass in an island manner in the beta phase besides the good effect of degassing and purifying the melt, has obvious influence on the appearance of the alpha phase in the microstructure of the brass, and plays an important role in the cutting performance of the alpha phase. Therefore, the addition amount of the element X in the present application is controlled to 0.003 to 0.20%.

Preferably, the brass contains an alpha phase and a beta phase, and the area fraction of the alpha phase is controlled to be 46-60%. The area contents of the alpha phase and the beta phase have important influence on the drilling performance and the riveting performance of the alloy. The area fraction of an alpha phase in the traditional H60 brass alloy is more than 70 percent, the rest is mainly a beta phase, the phase composition is beneficial to riveting but the machinability, particularly the drilling performance of a drill hole below phi 4mm is poor, the sticking of a tool exists, the temperature rise of the alloy is rapid, and the requirement on the cutting performance cannot be met.

Preferably, the more than 90% area fraction of the α phase is embedded in the β phase in islands in isolation. The connected alpha phases are easy to cause the non-uniformity of the structure and have poor mechanical property stability, so that the alpha phases are controlled to be insulatedly embedded in the beta phase matrix in an island manner, and each alpha phase is insulatedly and dispersedly embedded in the beta phase matrix, thereby improving the cutting performance.

Preferably, the brass has an α -phase size of 5 to 30 μm. The size of the alpha phase has important influence on the improvement of the drilling performance and the riveting performance of the alloy, the fine alpha phase is embedded in the beta phase, the fine alpha phase can refine the beta phase, the microstructure of the whole copper alloy is fine, the fine microstructure has higher strength and more stable mechanical property, and the cutting and riveting are facilitated; when the size of the alpha phase is more than 30 mu m, the alpha phase is easy to agglomerate and connect, has poor cutting performance and uneven mechanical property or poor stability and is easy to cause riveting and cracking, and when the size of the alpha phase is less than 5 mu m, the alpha phase is easy to appear in a needle form, and the needle alpha phase is easy to cause stress corrosion cracking.

Preferably, the area fraction of the acicular α phase in the brass α phase is controlled to 2% or less. The appearance of the brass alpha phase has important influence on the improvement of the drilling performance and the riveting performance of the alloy, the appearance of the alpha phase comprises the shape and the dispersed state, the alpha phase is mainly blocky and ideally nearly spherical in the application, but is generally difficult to control and basically irregularly blocky, the shape is favorable for cutting in the cutting process and can avoid the damage of a cutter, the connected alpha phase is easy to stick to the cutter, the temperature rise in the drilling process is fast, the key is unfavorable for cutting, if the control is improper, the acicular alpha phase appears, the acicular alpha phase is easy to cause the connection of the alpha phase, the acicular alpha phase cuts a substrate, the internal stress is increased, the crack is easy to occur in the riveting process, the acicular alpha phase is also favorable for cutting and cutting, the acicular alpha phase is avoided in the application, but is difficult to completely avoid in the actual process, therefore, the area fraction of the brass alpha phase is controlled below 2%, exceeding this range is disadvantageous in satisfying both cutting and riveting performance.

The second technical problem to be solved by the invention is to provide a preparation method of the lead-free-cutting brass.

The technical scheme adopted by the invention for solving the second technical problem is as follows: a preparation method of lead-free-cutting brass is characterized by comprising the following preparation processes: smelting → casting → extrusion → homogenizing annealing → acid washing → aisle drawing → softening annealing → finished product drawing; the extrusion temperature is 580-700 ℃.

The beta phase proportion in the structure can be reduced due to the excessively low extrusion temperature, and the alloy is not easy to cut; the extrusion temperature is too high, the tissue morphology of a high proportion of beta phase and a small amount of needle-shaped alpha phase appears in the tissue, and the beta phase is hard, so that on one hand, the abrasion of a cutting tool is accelerated, and the cutting performance of the alloy is deteriorated; on the other hand, the hardness of the alloy is high, and the riveting can crack for customers with riveting requirements; in order to control the proportion of alpha phase and beta phase in the brass matrix and control the area fraction of needle-shaped alpha phase in the brass alpha phase to be less than 2 percent, the extrusion temperature is 580-700 ℃ in the application.

Preferably, the homogenization annealing temperature of the brass is 300-550 ℃, and the time is 1-8 h.

The brass alloy needs to be added with a homogenizing annealing process, because the head and tail tissue shapes of the extrusion blank are different, the head of the extrusion blank is usually high in temperature, when the cooling speed is high, the needle-shaped alpha phase is usually easy to precipitate in a beta phase matrix, the cutting is not facilitated, in addition, the head and tail mechanical properties of the extrusion blank are also different, the performance is uneven, and the processing of customers is influenced; carry out homogenization annealing to the extrusion blank and can eliminate extrusion blank head and the tail tissue difference, make extrusion blank head and the tail mechanical properties even unanimous simultaneously, consequently, homogenization annealing temperature 300~550 ℃ in this application, time 1~8h, when the temperature is less than 300 ℃ or heat preservation time is less than 1h, the effect of eliminating extrusion blank head and the tail tissue difference is not obvious, when the temperature is higher than 550 ℃ or heat preservation time is higher than 8h, lead to the material internal structure unusually thick easily, especially the condition that alpha looks interconnect appears easily, deteriorate the cutting performance of alloy.

Preferably, the softening annealing temperature of the brass is 350-450 ℃, the temperature rise time is 30-60 min, and the heat preservation time is 120-300 min. According to the invention, the brass alloy is partially recrystallized in the annealing process by adopting annealing at a lower temperature of more than 350 ℃, so that most of work hardening is eliminated, the plasticity and the like of the alloy are improved, the risk of riveting cracking is favorably reduced, and meanwhile, the morphology of the structure obtained by extrusion is not obviously changed, namely, the condition that alpha phases in the structure are grown and connected with each other due to high-temperature annealing at more than 450 ℃ is avoided, so that the brass alloy has good cutting performance in the aspect of the morphology of the structure.

Preferably, the brass is melted by using 95% or more of used materials selected from at least one of brass scraps, red copper scraps, brass tin-plated scraps, and brass nickel-plated scraps. The old material generally contains a plurality of trace impurity elements which usually exist in the alloy matrix in the form of simple substances or compounds, and the trace impurity elements play a unique role in the alloy casting and processing process, on one hand, part of the trace impurity elements and compounds thereof are dispersed and distributed in the alloy matrix and can play a role in cutting and breaking chips; on the other hand, the trace impurity elements are used as nucleating agents to promote the alloy to form more crystal grains in the processes of solidification casting and thermal treatment recrystallization, or gather on the grain boundary to block the growth of the crystal grains, so that the effect of refining the crystal grains is achieved, and the cutting performance of the lead-free brass is improved. The alloy of the invention adopts more than 95 percent of old materials, which can absorb a large amount of scrap copper, reduce the cost of the free-cutting brass, fully exert the unique advantages of the scrap copper and improve the free-cutting performance.

Compared with the prior art, the invention has the advantages that: 1) the cost of the lead-free-cutting brass is reduced by controlling the content of Cu, and the phase composition of the brass alloy is changed by adding Sn and elements A and X, so that the combination of drilling performance and riveting performance is realized.

2) The temperature rise of the alloy is lower than 80 ℃ when the lead-free-cutting brass drills a phi 4.2 hole, the compression ratio of the alloy is lower than 80% when the alloy is riveted and cracked, and the lead-free-cutting brass has excellent drilling performance and riveting performance.

Drawings

FIG. 1 is a metallographic photograph of a sample of example 1 of the present invention.

Figure 2 photo of drill cuttings of example 1 of the present invention.

Fig. 3 is a photograph of drill cuttings of comparative example C3602.

Fig. 4 is a photograph of drill cuttings of comparative example H62.

Detailed Description

The invention is described in further detail below with reference to the accompanying examples.

Selecting 8 examples and two comparative examples (C3602 and H62), wherein the specific components are shown in the table 1, and the 8 examples are prepared according to the method disclosed by the invention and specifically comprise the following steps: smelting → casting → extrusion → homogenizing annealing → acid washing → aisle drawing → softening annealing → finished product drawing.

1) Smelting: the components of the embodiment are proportioned, all the old materials are adopted, and the old materials comprise: brass scrap, red copper scrap, brass tin-plating scrap and brass nickel-plating scrap, wherein the smelting temperature is as follows: at 900-1050 ℃, pouring all the melted raw materials into a power frequency holding furnace for casting after the tested components are qualified;

2) casting: the casting temperature is 980-1050 ℃, semi-continuous casting is adopted, and the sawing length of the cast ingot is 510 mm;

3) extruding: the number of extrusion heads is 2;

4) carrying out homogenization annealing;

5) acid washing: acid washing is carried out by adopting dilute sulfuric acid and hydrogen peroxide, after oxide skin on the surface layer of the blank is removed, the blank is washed clean by clear water, and is naturally dried after being soaked in an acid washing stabilizer;

6) stretching the passageway: the pass processing rate is 30 percent;

7) softening and annealing;

8) and (3) finished product stretching: the control is at 20%.

The drilling performance and the riveting performance of 8 examples and 2 comparative examples were tested.

And (3) detecting the drilling performance: drilling test is carried out on a numerical control lathe by adopting a phi 7mm bar, and the test conditions are as follows: the diameter of the drill bit: phi 4.2mm, lathe speed: 1200r/min, feed rate: and measuring the surface temperature of the workpiece by using a contact type temperature measuring instrument within 5s after the drilling is finished at 100 mm/min.

And (3) detecting riveting performance: machining a terminal with the length of 30mm by using a phi 4.77mm bar on a numerical control lathe, drilling a hole with the inner diameter phi of 3.0mm and the depth of 6mm at a riveting end of the terminal, slowly applying 1-3 KN pressure to the riveting end of a terminal riveting tester until cracks appear on the wall of the phi 3.0 hole, stopping applying the pressure, and recording the compression ratio of the change of the outer diameter of the hole when the riveting cracks.

It can be seen from table 3 that the tensile strength of examples 1 to 8 is 570MPa or more, the elongation is 10% or more, the hardness HV5 is 150 or more, the strength and hardness are significantly superior to those of C3602 and H62, and the elongation is equivalent to that of C3602.

As can be seen from fig. 1, the metallographic structure of example 1 is an α phase and a β phase, in which the α phase is in a bulk state, and more than 95% of the α phase is embedded in the β phase in isolated islands. As can be seen from FIG. 2, the drill cuttings of example 1 are powdery, and it can be seen from Table 3 that the temperature rise is 46 ℃, the drilling performance is excellent, the compression ratio of the alloy is 64% when the riveting cracking is performed, and the riveting performance is excellent; fig. 3 shows the drill cuttings of comparative example C3602, which are also in powder form, and the drilling performance and the riveting performance of example 1 are comparable, but the strength and hardness of C3602 are lower than those of example 1, so the overall performance of example 1 is better than that of C3602.

Fig. 4 is a photograph of drill cuttings of comparative example H62, which were long and were also poor in drilling performance and riveting performance, indicating poor machinability.

TABLE 1 chemical compositions of inventive and comparative examples

TABLE 2 Key Process parameter control and microstructure of the inventive examples

TABLE 3 Properties of inventive and comparative examples

Claims

1. The lead-free-cutting brass is characterized by comprising the following components in percentage by mass: 58.1 to 62.0%, Sn: 0.61-1.5%, Ni less than or equal to 0.1%, Fe less than or equal to 0.1%, Pb less than or equal to 0.09%, and element A and 0.003-0.20% of element X, the balance being Zn and inevitable trace elements, wherein the element A is selected from at least one of 0.02-0.5% of Te, 0.02-0.4% of Mg, 0.02-0.15% of P, and 0.1-1.5% of Si, and the element X is selected from Ti and/or Er; the brass contains an alpha phase and a beta phase, and the area fraction of the alpha phase is controlled to be 46-60%; the brass has an alpha phase of 5 to 30 μm in size.

2. The lead-free-cutting brass as recited in claim 1, wherein: more than 90% of the area fraction of the alpha phase is insulatively embedded in the beta phase as islands.

3. The lead-free-cutting brass as recited in claim 1, wherein: the area fraction of the acicular alpha phase in the brass alpha phase is controlled to be less than 2%.

4. A method for preparing the lead-free-cutting brass as claimed in any one of claims 1 to 3, wherein the preparation process of the brass comprises: smelting → casting → extrusion → homogenizing annealing → acid washing → aisle drawing → softening annealing → finished product drawing; the extrusion temperature is 580-700 ℃.

5. The method for preparing lead-free-cutting brass as claimed in claim 4, wherein: the homogenization annealing temperature of the brass is 300-550 ℃, and the time is 1-8 h.

6. The method for preparing lead-free-cutting brass as claimed in claim 4, wherein: the softening annealing temperature of the brass is 350-450 ℃, the temperature rise time is 30-60 min, and the heat preservation time is 120-300 min.

7. The method for preparing lead-free-cutting brass as claimed in claim 4, wherein: the brass is smelted by using more than 95% of old materials, wherein the old materials are selected from at least one of brass scraps, red copper scraps, brass tin-plated scraps and brass nickel-plated scraps.